The invention relates broadly to the utilization of a portion of the thermal energy in the hot water residing in the upper regions of a domestic or industrial hot water heater, either during the relatively short and intermittent kinetic mode, when hot water is being withdrawn from the tank, or during the static mode, i.e. during the long quiescent periods when hot water is not being withdrawn from the tank.
It is well known that in the interests of convenience and comfort, water heaters, even when well insulated, require that the heating unit be operated for more time than is necessary. Repeated heating cycles are required in order to maintain a considerable amount of water at an elevated temperature awaiting the demands of the user at any time during the day or night. This is especially true in the case of domestic water heaters.
Substantial quantities of water at high temperature, (up to 160.degree. F., or even more) migrate upwardly by convection from the heating source during each of the heating cycles, replacing the water that has cooled. The hottest water resides in the upper regions of the tank awaiting withdrawal through the hot water outlet. During the often long wait periods, conduction and radiation losses occur; and, when the hot water temperature falls to a minimum degree set by the user on the heater's thermostat, the heating cycle is renewed, lasting until the demand temperature is again reached, at which time the heat source is once more automatically turned off by the thermostat.
This on-off cycle is repeated, often several times during each 24-hour period. Efficiency is sacrificed to the convenience of always having very hot water available, and heat is unnecessarily wasted since heat losses mount exponentially as the demand temperature is increased.
A search of the prior art was made to ascertain what, if any, technology had developed to ameliorate the inefficiency inherent in a system of this kind.
The following six patents were disclosed:
______________________________________ 3,926,743 Cywin 4,242,870 Searingen et al 4,033,141 Gustafsson 4,270,350 Chevalier 4,100,744 De Munari 4,272,962 Viscovich et al ______________________________________
Although these patents reveal various systems for utilizing heated fluids in the production of usable mechanical or electrical energy, none discloses any arrangement readily adaptable to the particular problems which exist in a hot water heater; nor do they suggest extracting useful work from the hot water which would otherwise be lost through conduction and radiation during the quiet hours.